Along with a heightened degree of exposure precision in exposure apparatuses, a stage used for an exposure apparatus has been proposed as a positioning apparatus for positioning an exposure target at a predetermined position with high precision in a short time. The stage (FIG. 4A) comprises: an XY stage for positioning the exposure target on the XY plane by moving the stage at high speed, and a six-axis precision stage provided on top of the XY stage for adjusting a position and a rotation angle of the target on the plane.
The XY stage 6 on the exposure apparatus stage includes an X linear motor 2 for driving the stage in the X-axis direction on the stage table 1, and a Y linear motor 3 for driving the stage in the Y-axis direction. Each of these linear motors serves as a driving source in the X and Y direction. The XY stage 6 is supported by a Y slider 5 and an X slider 4. On the XY stage 6, which comes into contact with slider guides (15, 16), air pads (9, 11) are provided. From the air pads, compressed air is issued to the guide members, thereby forming an air layer between the guide members and the sliders. Accordingly, friction in the sliding portions of the X and Y sliders (4, 5) is reduced, enabling the respective sliders (4, 5) to slide.
The XY stage 6 is driven at high speed and positioned at a target position with coarse precision. Further, in order to adjust the position and rotation angle of the exposure target with high precision, a precision stage 7 is arranged on top of the XY stage 6. By driving the precision stage 7, the exposure target is positioned at a predetermined exposure position (target position) with high precision.
The precision motion mechanism of the precision stage employs precision linear motors for six axes (three axes in the translational directions and three axes in the rotational directions). By driving the linear motors, the position of the precision stage with respect to the translational directions and the rotational posture of the precision stage with respect to each axis are adjusted.
FIG. 4B shows in detail an arrangement of the six-axis precision linear motors provided for driving the precision stage 7. As shown in FIG. 4B, the precision linear motors consist of: two X precision linear motors 100, two Y precision linear motors 110, and three Z precision linear motors 120. In order to realize motion in the directions of six axes, seven linear motors are arranged.
Each precision linear motor comprises: an oval flat coil (110d, 120d, and so on) having a hollow core, magnets (110c, 120c, and so on) provided in a way to sandwich the flat coils from both sides, and yokes (110b, 120b, and so on). The precision linear motors employ the so-called Lorentz force. Each linear motor generates thrust in a direction (direction of the arrows in FIG. 4B), which is orthogonal to the straight line portion of each oval coil, on the plane parallel to the flat surface of each oval flat coil.
With regard to the X precision linear motor 100, the flat surface of the oval coil is parallel to the XZ plane and the straight line portion of the oval coil is parallel to the Z axis. With regard to the Y precision linear motor 110, the flat surface of the oval coil is substantially parallel to the YZ plane and the straight line portion of the oval coil is parallel to the Z axis. With regard to the Z precision linear motor 120, the flat surface of the oval coil is substantially parallel to the YZ plane and the straight line portion of the oval coil is parallel to the Y axis. By virtue of this configuration, thrust is generated in the X, Y, and Z directions. The yokes are moved based on the thrust, thereby adjusting the position and rotation angle with respect to the direction of each plane (XY plane, YZ plane, ZX plane) and the rotational directions (rotation about the X axis, Y axis, Z axis).
Each coil of the respective linear motors is fixed to a top plate 14 of the XY stage 6 through a coil frame (e.g., 110e of the Y precision linear motor 110). Each magnet (e.g., 110c of the Y precision linear motor) and yoke (e.g., 110b of the Y precision linear motor) are fixed to a precision-motion top plate 21 through a yoke fixing member (110a of the Y precision linear motor).
The stage mechanism shown in FIG. 4A having the above-described configuration has the following advantages. The stage mechanism has a lighter transfer mass of the driving axis, compared to a stage mechanism having one stage moving in one axis direction and having another stage thereupon moving in another axis direction (e.g., X stage driving in X direction arranged on top of Y stage driving in Y direction). Another advantage is in that the linear motors, which become the source of heat, can be arranged far from a wafer.
The exposure apparatus stage, incorporating the six-axis precision stage employing the Lorentz force on top of the XY stage, is advantageous because highly precise position and rotation angle control can be achieved during a long stroke of the stage.
Meanwhile, along with the downsizing of patterns exposed by exposure apparatuses, attention is given to a charged-particle-beam exposure apparatus, e.g., an electron beam (EB) exposure apparatus, an ion beam exposure apparatus or the like. If the configuration of the conventional six-axis precision motion mechanism is to be employed in the charged-particle-beam exposure apparatus, it causes two problems: (a) it is prone to leak magnetic flux; and (b) the size of the precision linear motor becomes large.
Although the stationary members of the precision linear motors (100, 110, 120 in FIG. 4B) have a closed magnetic circuit, magnetic flux easily leaks from both sides of the magnets. Also, the magnetic field generated by the coils tends to leak outside. In other words, since permanent magnets are used, magnetic flux is always generated even at the time of not generating a driving force for precision motion, and causes an external leakage. Such magnetic flux leakage disturbs the electron-optical system of the EB exposure apparatus, causing deterioration in the precision of electron beam rendering.
Furthermore, the typical size of the precision linear motor is about 100 mm (length)×40 mm (width), and 50 mm (depth). In a case where a magnetic shield is provided in order to seal the aforementioned magnetic flux leakage, the size of the precision linear motor including the magnetic shield becomes larger than the typical size, and the occupying area of the linear motors is enlarged.
Furthermore, since it is extremely difficult to provide a threefold or fourfold shield in the linear motor of the aforementioned size, it is substantially impossible to employ the conventional six-axis precision stage in the charged-particle-beam exposure apparatus.